What is best traps of petroleum?

Good reservoir with good permeability and sealing cap (cap rock) with low permeability is very good trap. In all traps are classified into: structural traps, strati graphictraps and may be combined from both. other trap may be from as fractured traps like i basement rocks.

Geologicaly speaking I would say it is an anticline with good grain quality (sandstone) and good seals and water aquifer in the bottom. 

The best traps of petroleum is the Structural traps:

The anticline traps. These are preferential sites of oil and gas. And the fault trap.

Anticline Fold Trap. this type of trap is by far the most significant to the hydrocarbon industry.

Structural trap.

the amount of haydrocarbon in any trap depend on different propery and chaerteristics so in some cases it also depend on trap to taps.

Structural Traps having an Anticline is acting as a best trap

an anticlinal is the best trap of petroleum

anticlinal trap A fold structure with an arch of non-porous rock overlying porous strata (reservoir rock), providing a trap in which oil, gas, or water may accumulate

Structural Traps are the best traps with no permability.

Structural traps  such as Anticline with sandstone reservoir rock ,good sealing rocks and water drive mechanism

A good trap for petroleum is a swamp full of reeds and petroleum digesting bacteria and other organisms which break down the complex chemical chain of organic molecules.